The present invention is related to the confidentiality of television signal transmissions, and more particularly to the protection of TV signal transmissions from unauthorized reception. The environment in which the present invention may be widely applicable, and in the context of which the invention will be described herein, is that of subscriber television and TV program distribution.
Subscriber television systems are becoming increasingly widespread wherein TV signals are sent out via a cable network or over the air and are intended for reception and viewing by only those subscribers who have paid a monthly fee. With the increase in subscriber television systems has also come an increase in the number of people attempting to receive and display the premium television programs without payment. Thus, there is a need for more sophisticated security techniques for preventing such unauthorized reception.
Many existing subscriber television systems utilize, directly or indirectly, signals transmitted via satellite, and it is becoming quite common for non-paying individuals to receive and display the premium television programs via television receive only (TVRO) antennas, thus resulting in a substantial loss of revenue for the distributors of the subscription television programs. In addition, various direct satellite broadcast television systems are currently being proposed wherein subscription television programs will be broadcast directly via satellite to individual subscriber homes. These subscription satellite television (SSTV) systems will be quite vulnerable to unauthorized reception, and an effective security technique is therefore highly desirable.
The purpose of a security subsystem for an SSTV system is to protect the distributor's business interest and, accordingly, the following objectives should be achieved:
(1) To prevent a non-subscriber from receiving intelligible video and audio signals by using a regular home television set;
(2) To prevent a delinquent subscriber from receiving intelligible video and audio signals by using the SSTV decoder;
(3) To prevent a legitimate subscriber from receiving intelligible video and audio signals of unsubscribed SSTV channels or programs;
(4) To discourage an average technician from building his own receiver capable of obtaining acceptable quality video and audio signals;
(5) To discourage a small unauthorized business concern from manufacturing and marketing devices which are capable of receiving and displaying acceptable quality video and audio signals from the SSTV channels; and
(6) To allow a legitimate subscriber to receive and display high quality video and audio signals from the subscribed channels or programs.
It would also be highly desirable to achieve the above objectives at a reasonable cost.
A number of security systems for CATV exist, most of which involve the suppression or removal of the horizontal sync pulses from the video signal before transmission, and the recovery of the sync pulses at the receive end. These techniques will prevent people without the sync recovery circuits from receiving and displaying the programs and may therefore achieve objectives (1) and (6) above, but .[.those.]. .Iadd.these .Iaddend.security systems do not achieve objectives (2) and (3) and, since sync recovery circuits are relatively easily designed and manufactured, also do not satisfy objectives (4) and (5).
More sophisticated techniques may include additional intelligence in the subscriber's decoder box, including the capability of receiving commands from a control center which are specifically addressed to an individual subscriber and are used to turn on or off some or all of the channels. These more sophisticated security techniques may succeed in achieving objectives (1)-(3) and (6), but still do not satisfy objectives (4) and (5). For example, most of these techniques involve the checking of a password, and a particular channel is turned on only if the password is matched. This could be relatively easily by-passed by modifying the subscriber's decoder box or building a separate box with all of the necessary features except the on/off switch. Further, subscribers may also be able to tamper with the decoder box to receive more programs than are actually paid for.